The present invention relates to the preparation of 2-aminomuconate from 2-aminophenol.
2-Aminomuconate is an intermediate in the oxidative metabolism of tryptophan in mammals. The compound is not commercially available, and studies of its metabolism have been prevented by the lack of a chemical synthesis and the instability of the molecule.
Interest in the catabolic pathway of degradation of L-tryptophan has grown steadily over the last decade due to the role of quinolinate and other metabolites in several neuropathological conditions. The neurotoxin, quinolinate, is formed nonenzymatically from 2-amino-3-carboxymuconic semialdehyde in mammalian tissues. 2-Amino-3-carboxymuconic semialdehyde is enzymatically converted to 2-aminomuconate (2-aminohexa-2,4-diene-1,6-dioate), via 2-aminomuconic semialdehyde. The effect of the enzymatic pathway on non-enzymatic accumulation of quinolinate in the central nervous system has not been investigated. Furthermore, 2-aminomuconate itself may also have a significant neurophysiological function in the central nervous system by virtue of the fact it is a dicarboxylic xcex1-amino acid, and is similar to other neural excitatory amino acid agonists or antagonists. Another concern is the neurotoxicity of ammonia, released from 2-aminomuconate during the metabolism of tryptophan in the central nervous system. The lack of the availability of 2-aminomuconate has severely limited experimental approaches to investigation of these aspects of mammalian neurophysiology.
Recently, we found that 2-aminomuconate is one of the intermediates in the pathway for the biodegradation of nitrobenzene by the bacterium Pseudomonas pseudoalcaligenes JS45. 2-Aminomuconate is produced from 2-aminophenol by the action of 2-aminophenol 1,6-dioxygenase and 2-aminomuconic semialdehyde dehydrogenase. We have prepared 2-aminomuconate with these two enzymes either in crude extracts or in the fractions from a DEAE-Sepharose column, and separated it by anion exchange chromatography for use in investigating the properties of 2-aminomuconate deaminase from P. pseudoalcaligenes JS45. However, attempts to prepare the material in large quantities for general use failed because the partially purified dioxygenase was unstable even during storage at xe2x88x9270xc2x0 C. In crude extracts the dioxygenase was relatively stable, but the presence of 2-aminomuconate deaminase precluded accumulation of 2-aminomuconate.
Accordingly, it is an object of the present invention to provide an improved method for the preparation of 2-aminomuconate.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the present invention there is provided an improved method for the preparation of 2-aminomuconate. The method of this invention comprises adding 2-aminophenol to a mixture of 2-aminophenol 1,6-dioxygenase, 2-aminomuconic semialdehyde dehydrogenase and AND+ (nicotinamide adenine dinucleotide, oxidized form) in a buffer, and recovering a fraction containing 2-aminomuconate from the mixture.